Major Sources Of Volatile Organic Compounds Research Articles

Reducing southern California ozone concentrations in the year 2050 under a low carbon energy scenario

Recent studies predict that ozone (O3) concentrations within major California cities in the year 2050 will continue to violate the 8-h O3 standard despite the adoption of low-carbon energy. This O3 penalty largely stems from persistent NOx-rich chemistry within urban cores that causes O3 concentrations to increase when traditional combustion sources are replaced by renewable energy sources. Here we employ a Chemical Transport Model (CTM) equipped with a novel O3 source apportionment technique to better understand O3 formation and to design supplemental control measures to complement Greenhouse Gases (GHG) reduction strategies in California. Two base scenarios were analyzed: (i) a 2050 “business-as-usual” (BAU) scenario with O3 violations on 43% of simulated days, and (ii) a 2050 Greenhouse Gases reduction (GHGAi) scenario with O3 violations on 32% of simulated days. The source apportionment results of the GHGAi scenario identified offroad equipment & rail, marine vessels & aircraft, and industrial & agricultural emissions as the major NOx sources that contributed to the O3 violations, while boundary conditions & initial conditions (BCIC) and biogenic emissions were identified as the major volatile organic compounds (VOCs) sources. Despite a HCHO/NO2 ratio (FNR) suggesting that the SoCAB is in a VOC-limited chemical regime, the major VOC sources that contribute to O3 formation are not controllable. Therefore, complementary O3 control strategies are proposed that focus on NOx emissions within the GHGAi scenario. Three cumulative Supplemental Control Steps were evaluated. Control Step I reduced emissions from off-road equipment & rail, and marine vessels & aircraft (65% NOx emissions reduction relative to GHGAi). Control Step II expanded the measures in Control Step I by reducing emissions from industrial and agricultural sources (cumulative 73.6% NOx emissions reduction relative to GHGAi), while Control Step III extended the amount of control applied to all sources covered in Control Steps I and II (cumulative 85.4% NOx emissions reduction relative to GHGAi). All three Control Steps lowered O3 concentrations significantly in the SoCAB, with residual O3 violations mainly predicted in non-populated wilderness areas. The significant reductions in O3 produced by the Supplemental Control Steps decreased the predicted incidence of hay fever/rhinitis, asthma, and all-cause mortality by an order of magnitude compared to the transformation from the BAU to GHGAi scenario. The predicted public health savings associated with the Supplemental Control Steps are valued at $19.70–30.36B/yr.

Pollution characteristics and secondary formation potential of volatile organic compounds in the multi-industrial city of Ulsan, Korea

The secondary formation of ozone and aerosols due to volatile organic compounds (VOCs) has drawn increased attention in Ulsan, a multi-industrial city in South Korea. In this study, 52 VOCs were measured at 40 sites in four industrial (petrochemical, nonferrous, automobile, and shipbuilding) complexes and five urban sites using passive air samplers. The concentration of aromatics (44.6 μg/m3) accounted for 70.3% of the total VOC concentration (63.4 μg/m3), which was significantly higher than those of alkanes (27.5% and 17.4 μg/m3) and alkenes (2.15% and 1.37 μg/m3). The highest concentrations of total VOCs and aromatics were observed at the shipbuilding industrial complex, whereas the concentration of alkanes and alkenes was the highest in the petrochemical industrial complex. The positive matrix factorization (PMF) model suggested five major VOC sources in urban areas: (1) petrochemical production processes, (2) fuel combustion and evaporation, (3) urban emissions sources, (4) solvent use, and (5) painting and metal surface coating. The PMF result indicated that the distances from the four industrial complexes substantially affected VOC pollution in the urban areas. Moreover, aromatics (e.g., m,p-xylenes, toluene, ethylbenzene, o-xylene, and 1,2,4-trimethylbenzene) exhibited higher ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP), which were mainly emitted from solvent use and painting in the shipbuilding and automobile industrial complexes. The petrochemical industrial complex close to densely populated urban areas also contributed significantly to secondary formation potential. In conclusion, our study revealed that elevated levels of aromatics were associated with increased OFP and SOAFP. Additionally, the four industrial complexes exhibited varying impacts on pollution characteristics in urban areas. These findings have practical implications, as they can inform the development of industry-specific management strategies for mitigating VOC pollution and secondary formation in multi-industrial cities.

Soil uptake of VOCs exceeds production when VOCs are readily available

Volatile organic compounds (VOCs) are reactive gaseous compounds with significant impacts on air quality and the Earth's radiative balance. While natural ecosystems are known to be major sources of VOCs, primarily due to vegetation, soils, an important component of these ecosystems, have received relatively less attention as potential sources and sinks of VOCs. In this study, soil samples were collected from two temperate ecosystems: a beech forest and a heather heath, and then sieved, homogenized, and incubated under various controlled conditions such as different temperatures, oxic vs. anoxic conditions, and different ambient VOC levels. A dynamic flow-through system coupled to a proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS) was used to measure production and/or uptake rates of selected VOCs, aiming to explore the processes and their controlling mechanisms. Our results showed that these soils were natural sources of a variety of VOCs, and the strength and profile of these emissions were influenced by soil properties (e.g. moisture, soil organic matter), oxic/anoxic conditions, and temperature. The soils also acted as sinks for most VOCs when VOC substrates at parts per billions levels (ranging between 0.18 and 68.65 ppb) were supplied to the headspace of the enclosed soils, and the size of the sink corresponded to the amount of VOCs available in the ambient air. Temperature-controlled incubations and glass bead simulations indicated that the uptake of VOCs by soils was likely driven by microbial metabolism, with a minor contribution from physical adsorption to soil particles. In conclusion, our study suggests that soil uptake of VOCs can mitigate the impact of other significant VOC sources in the near-surface environment and potentially regulate the net exchange of these trace gases in ecosystems.

Leaf-level metabolic changes in response to drought affect daytime CO2 emission and isoprenoid synthesis pathways.

In the near future, climate change will cause enhanced frequency and/or severity of droughts in terrestrial ecosystems, including tropical forests. Drought responses by tropical trees may affect their carbon use, including production of volatile organic compounds (VOCs), with implications for carbon cycling and atmospheric chemistry that are challenging to predict. It remains unclear how metabolic adjustments by mature tropical trees in response to drought will affect their carbon fluxes associated with daytime CO2 production and VOC emission. To address this gap, we used position-specific 13C-pyruvate labeling to investigate leaf CO2 and VOC fluxes from four tropical species before and during a controlled drought in the enclosed rainforest of Biosphere 2 (B2). Overall, plants that were more drought-sensitive had greater reductions in daytime CO2 production. Although daytime CO2 production was always dominated by non-mitochondrial processes, the relative contribution of CO2 from the tricarboxylic acid cycle tended to increase under drought. A notable exception was the legume tree Clitoria fairchildiana R.A. Howard, which had less anabolic CO2 production than the other species even under pre-drought conditions, perhaps due to more efficient refixation of CO2 and anaplerotic use for amino acid synthesis. The C. fairchildiana was also the only species to allocate detectable amounts of 13C label to VOCs and was a major source of VOCs in B2. In C. fairchildiana leaves, our data indicate that intermediates from the mevalonic acid (MVA) pathway are used to produce the volatile monoterpene trans-β-ocimene, but not isoprene. This apparent crosstalk between the MVA and methylerythritol phosphate pathways for monoterpene synthesis declined with drought. Finally, although trans-β-ocimene emissions increased under drought, it was increasingly sourced from stored intermediates and not de novo synthesis. Unique metabolic responses of legumes may play a disproportionate role in the overall changes in daytime CO2 and VOC fluxes in tropical forests experiencing drought.

Summer O3 pollution cycle characteristics and VOCs sources in a central city of Beijing-Tianjin-Hebei area, China

One of the major pollutants influencing urban air quality in China is O3. O3 is the second most important pollutant affecting air quality in Shijiazhuang, which is the third largest city in the Beijing-Tianjin-Hebei area and the provincial capital of Hebei province. To fully understand the characteristics of O3 and volatile organic compounds (VOCs), which are O3 precursors, and the role of VOCs to ozone formation, we measured the hourly concentrations of O3 and 85 VOCs in Shijiazhuang continuously from January to November 2020, and the concentration characteristics of both together with the chemical reactivity and sources of VOCs were analyzed from a seasonal perspective. The O3 concentration in Shijiazhuang showed a phenomenon of high summer and low winter, and the VOCs showed a phenomenon of high winter and low spring. In the summer when the O3 exceedance rate is the highest, the time-domain variation characteristics of O3 were analyzed by wavelet analysis model, and the main periods controlling the O3 concentration variation in Shijiazhuang in summer 2020 were 52 days, 32 days, 19 days and 12 days. The maximum incremental reactivity (MIR) and propylene equivalence method indicated ethene, propylene and 1-pentene were common substances in the top five species of each season. The T/B, Iso-p/N-p, Iso-p/E, N-p/E, and positive matrix factorization (PMF) model showed that industrial source (18.62%–22.03%) and vehicle emission (13.20%–17.69%) were the major VOCs sources in Shijiazhuang. Therefore, to control the O3 concentration in Shijiazhuang, it is necessary to decrease alkenes emissions as well as VOCs from industrial source and vehicle emission.

Significant impact of VOCs emission from coking and coal/biomass combustion on O3 and SOA formation in taiyuan, China

Volatile organic compounds (VOCs) are the significant precursors of ozone (O3) and secondary organic aerosols (SOA) in fine particles (PM2.5). To effectively control O3 and PM2.5 pollution, VOCs were measured in Taiyuan during the prevailing seasons of pollution: summer (July 16 to 29), autumn (October 21 to November 5), and winter (December 26, 2021, to January 4, 2022). The highest total VOC (TVOC) concentrations were observed in winter (30.62 ± 14.81 ppbv), followed by autumn (25.98 ± 12.83 ppbv) and summer (11.43 ± 8.01 ppbv). Alkanes and alkenes were the dominant species, which together accounted for 78.35%–85.35% of TVOC concentration during the observation period. The ozone formation potential (OFP) and secondary organic aerosol production potential (SOAP) were used to estimate the contribution of VOC species and sources to O3 and SOA production. Alkenes were the dominant contributor to OFP, accounting for 71.88%–80.82%, while aromatics were the primary contributor to SOAP, accounting for 92.66%–96.14%. Based on the positive matrix factorization (PMF) model results, coking sources (21.89%) and coal/biomass combustion (22.86%) were not only the major VOC sources during the observation, but also contributed significantly to OFP (64.16%–81.38%) and SOAP (57.09%–75.28%), respectively. According to the potential source area of TVOC, and the VOCs, OFP and SOAP concentration of each source under different trajectories, VOC contributions were increasingly coming from the coking sources and coal/biomass combustion in local and southwest of Taiyuan. Consequently, it is essential to control the VOC emissions from coking sources and coal/biomass combustion in local and southwest regions to alleviate PM2.5 and O3 pollution in Taiyuan.

Distribution characteristics, air-water exchange, ozone formation potential and health risk assessments of VOCs emitted from typical coking wastewater treatment process

Coking industry has been considered as important source of volatile organic compounds (VOCs) emissions. However, few studies have emphasized the occurrence and adverse effects of VOCs from coking wastewater treatment processes. In this research, pollution profiles of both air and water phase VOCs in a typical coking wastewater treatment plant were investigated in terms of distribution characteristics, air-water exchange, ozone formation potential (OFP) and associated human health risks. Thirty VOCs were detected in the air phase, in which benzene and naphthalene were found to be the major VOCs with total contribution of 87.81 %. Nineteen VOCs were detected in the water phase, in which benzene, naphthalene and toluene contribute most to total VOCs with total contribution of 75.1 %. The regulating tank (RT) was the major source of VOCs, and the emission rate of total VOCs from all unites was 2711.03 g/d with annual emission of 0.99 t. The emission factor was estimated to be 1.36 g VOCs/m3 wastewater. The air-water exchange was assessed using the Fugacity model, and water-to-air volatilization was predominant based on the net flux of air-water exchange. OFP evaluated by emission factor indicated that the total OFP in RT was the highest (1.52 g O3/m3 wastewater), and toluene contributed 41.8 % of the total OFP, followed by naphthalene accounting for 38.7 % The total carcinogenic risks were in the range of 8.60 × 10−6 to 2.18 × 10−3, in which the RT exceeded the significant risk threshold (>1 × 10−4). The non-carcinogenic risks of hazard quotient value in RT also exceeded the risk threshold (>1), and naphthalene was the major contributor accounting for 79.02 %. These results not only provided comprehensive knowledge on pollution profiles and environmental risks of VOCs during coking wastewater treatment processes, but also facilitated the implement of VOCs regulation and occupational health protection strategies in coking industries.

Vehicle Emission Changes in China under Different Control Measures over Past Two Decades

Vehicle emissions have become a significant source of air pollution in urban cities, especially in China. Mobile sources account for 45% of local fine particle emissions in the Chinese capital Beijing. The Beijing–Tianjin–Hebei (BTH) area, one of China’s most representative urban clusters, is suffering from severe air pollution. With the rapid growth of vehicle ownership in the past two decades, vehicle emissions in China have also undergone great changes under various management measures. The BTH region is also a place where mobile source emission management was carried out earlier. It is of important research value to understand the evolution trend of the vehicle ownerships in the BTH region and the actual effects of various management measures for the control of vehicle emissions. Due to the imperfect evaluation of the current vehicle emission limitation measures from 2000 to 2019, the vehicle emission inventory of the BTH region was established, and the major control measures in the BTH region were evaluated. Results showed that the vehicle ownership has been increasing year by year over the past 20 years, from 2.39 million in 2000 to 25.32 million in 2019, with an average annual growth rate of 13.24%. However, the pollutants discharged by motor vehicles showed a trend of first rising and then falling due to various measures except CO2. The unsynchronized control measures have resulted in huge differences in vehicle growth trends and emissions among Beijing, Tianjin and Hebei. The emissions of carbon monoxide (CO), volatile organic compounds (VOCs), nitrogen oxides (NOX), and particulate matter (PM10) in Beijing showed a trend of increasing first and then decreasing. The changes in these pollutants in Tianjin were similar to those in Beijing, but there was a secondary increase for NOX and PM10 in the later period. The discharge of all pollutants in Hebei Province showed a growing trend except sulfur dioxide (SO2). The major emission source of CO and VOCs in BTH was PCs, and the contribution rate of PCs to VOCs, reached 86.0–89.6% in 2019. Heavy-duty trucks (HDTs) and buses were the main sources of NOX emissions, contributing 78.2–85.4% of NOX in 2019. Eliminating high emission vehicles was the best control measure in the BTH Region, which had a good emission reduction effect on all pollutants. For sustainable development of the BTH region, it is suggested that Beijing, Tianjin and Hebei province implement vehicle control policies simultaneously and establish a joint management mechanism.

The Battle of Battle Creek: Seeking Superfund Justice.

An early epidemiologic study on groundwater contamination in the United States took place at an Environmental Protection Agency (EPA) Superfund site in Battle Creek Michigan. Volatile organic compounds (VOCs) consisting of chlorinated 2-carbon solvents were identified in private and municipal wells serving several communities. One major source of VOC was a solvent recovery operation near the municipal well field. The study modeled the VOC plume and investigated mortality and morbidity outcomes thought to be related to the VOC. Although quite statistically significant excess mortality and morbidity (hospital discharge and survey questionnaire) outcomes were observed, there were few associations with VOC water cumulative metrics. Another potentially dominant class of exposures could arise in VOC water contamination episodes from the diverse contents of spent solvents generated in multiple, local manufacturing activities. The findings at Battle Creek are re-interpreted in this light and the implications for Superfund-like investigation strategy and reporting are discussed.

Chemical Reaction Activity and Source Apportionment of Atmospheric VOCs in Summer in Dalian

To investigate the characteristics and source apportionment of atmospheric volatile organic compounds (VOCs) in Dalian, the concentration level, composition characteristics, reaction activity, and source apportionment of atmospheric VOCs in Dalian were analyzed based on high-resolution online observation VOCs data from June to August 2020. The results showed that the average φ(VOCs) was (10.21±5.71)×10-9, in which alkanes accounted for 66.35%, alkenes for 11.89%, alkynes for 7.75%, and aromatics for 14.01%. VOCs and NOx were high at night and low during the day, whereas the change trend of O3 was opposite. Considering the species activity, it was determined that toluene, ethylene, m/p-xylene, 1-hexene, n-butane, isopentane, n-pentane, and isoprene were the key species affecting atmospheric VOCs in Dalian. Priority control of olefin and aromatic hydrocarbon emissions is the key to improve O3 pollution in summer in Dalian. By applying the positive matrix factorization (PMF) model, six major VOCs sources were extracted, namely traffic sources (26.38%), combustion sources (22.75%), industrial emission sources (17.09%), solvent usage sources (14.59%), natural sources (11.72%), and others (7.47%). The emissions of traffic sources and combustion sources are the key pollution sources for O3 prevention and control in Dalian in summer.

Characterization, reactivity, source apportionment, and potential source areas of ambient volatile organic compounds in a typical tropical city

Based on one-year observation, the concentration, sources, and potential source areas of volatile organic compounds (VOCs) were comprehensively analyzed to investigate the pollution characteristics of ambient VOCs in Haikou, China. The results showed that the annual average concentration of total VOCs (TVOCs) was 11.4 ppbV, and the composition was dominated by alkanes (8.2 ppbV, 71.4%) and alkenes (1.3 ppbV, 20.5%). The diurnal variation in the concentration of dominant VOC species showed a distinct bimodal distribution with peaks in the morning and evening. The greatest contribution to ozone formation potential (OFP) was made by alkenes (51.6%), followed by alkanes (27.2%). The concentrations of VOCs and nitrogen dioxide (NO2) in spring and summer were low, and it was difficult to generate high ozone (O3) concentrations through photochemical reactions. The significant increase in O3 concentrations in autumn and winter was mainly related to the transmission of pollutants from the northeast. Traffic sources (40.1%), industrial sources (19.4%), combustion sources (18.6%), solvent usage sources (15.5%) and plant sources (6.4%) were identified as major sources of VOCs through the positive matrix factorization (PMF) model. The southeastern coastal areas of China were identified as major potential source areas of VOCs through the potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) models. Overall, the concentration of ambient VOCs in Haikou was strongly influenced by traffic sources and long-distance transport, and the control of VOCs emitted from vehicles should be strengthened to reduce the active species of ambient VOCs in Haikou, thereby reducing the generation of O3.

Characteristics, Sources, and SOAP of VOCs During Winter in Jiyuan

Haze pollution events often occur in the heavy industry city of Jiyuan. Volatile organic compounds (VOCs) are the precursors of secondary organic aerosol (SOA), which accounts for 15%-20% of particulate matter (PM2.5). Here, PM2.5, O3, VOCs, and trace gases were monitored by using online instruments in Jiyuan from December 1st to 31st. The characteristics, sources, and secondary organic aerosol potential (SOAP) of VOCs were analyzed. The mean concentrations of TVOC were (54.3±27.5)×10-9. Alkanes, halocarbons, and alkynes were the predominant VOCs. The positive matrix factorization model was used to identify and apportion VOCs sources. Eight major sources of VOCs were identified, which included liquefied petroleum gas (LPG) or natural gas (NG), the polyvinyl chloride (PVC) industry, vehicular exhaust, the coking industry, solvent usage, industry, technological process, and fuel evaporation. The SOAP of aromatics was the largest. Among them, BTEXs were the dominant contributors to SOAP.

VOC characteristics and their source apportionment in a coastal industrial area in the Yangtze River Delta, China

Volatile organic compounds (VOCs) are important precursors of secondary organic compounds and ozone, which raise major environmental concerns. To investigate the VOC emission characteristics, measurements of VOCs based on proton transfer reaction-mass spectrometry during 2017 were conducted in a coastal industrial area in Ningbo, Zhejiang Province, China. Based on seasonal variation in species concentration, the positive matrix factorization (PMF) receptor model was applied to apportion the sources of VOCs in each season. The PMF results revealed that unknown acetonitrile source, paint solvent, electronics industry, biomass burning, secondary formation and biogenic emission were mainly attributed to VOC pollution. Biomass burning and secondary formation were the major sources of VOCs and contributed more than 70% of VOC emissions in spring and autumn. Industry-related sources contributed 8.65%–31.2% of the VOCs throughout the year. The unknown acetonitrile source occurred in winter and spring, and contributed 7.6%–43.73% of the VOC emissions in the two seasons. Conditional probability function (CPF) analysis illustrated that the industry sources came from local emission, while biomass burning and biogenic emission mainly came from the northwest direction. The potential source contribution function (PSCF) model showed that secondary formation-related source was mainly from Jiangsu Province, northeastern China and the surrounding ocean. The potential source areas of unknown acetonitrile source were northern Zhejiang Province, southern Jiangsu Province and the northeastern coastal marine environments.

High-spatial-resolution VOCs emission from the petrochemical industries and its differential regional effect on soil in typical economic zones of China

Volatile organic compounds (VOCs) are toxic to the ecological environment. The emission of VOCs into the atmosphere has already caused attention. However, few studies focus on their regional effects on soil. As a major VOCs source in China, research on the effect of petrochemical industry on the environment is urgent and essential for regional control and industrial layout. This study established national VOCs emission inventory of five petrochemical sub-industries and spatial distribution based on consumption of raw material or products' yield and 28,888 factories. The VOCs emissions showed continuously increasing trend from 2008 to 2019, with cumulative 1.83 × 107 t, wherein these from rapid economic development zones accounted for 66.10%. The detected concentrations of VOCs in various industries combined with meteorological parameters were used in Resistance Model to quantify regional dry deposition. Higher concentrations of 111 VOC species were 238.27, 260.01, 207.54 μg·m−3 from large-scale enterprises for crude oil and natural gas extraction, oil processing, synthetic rubber and resin, leading to higher deposition ratios of 0.81%–0.94%, 0.70%–0.81%, 1.50%–1.75% in rapid economic development zones, respectively. The regional climate condition played a dominant role. Annual VOCs dry deposition amount in rapid economic development zones was calculated to be totally 6.38 × 103 t using obtained deposition ratios and emissions, with 3.21 × 103 t in Bohai Economic Rim (BER), 2.42 × 103 t in Yangtze River Economic Belt (YREB), 748.43 t in Pearl River Delta (PRD). Generally, crude oil and natural gas extraction, oil processing, synthetic rubber and resin contributed 13.09%, 57.77% and 29.14%, respectively. The proportion of synthetic rubber and resin for dry deposition increased by 5.04%–18.81% compared with VOCs emissions in BER and YREB. In contrast, it declined from 45.52% for emission to 29.86% for deposition due to absolute dominance of small-scale enterprises in PRD. Overall, VOCs control from oil processing was significant, especially in BER.

Sources and Seasonal Variance of Ambient Volatile Organic Compounds in the Typical Industrial City of Changzhi, Northern China

Volatile organic compounds (VOCs) emitted from industrial processes, which are major emission sources of air pollutants, could cause significant impacts on air quality. However, studies on the comprehensive analysis from sources contributing to the health risk perspective regarding ambient VOCs in industrial cities are limited. In this study, VOC samples were collected from 15 April 2018 to 19 October 2018 in Changzhi, a typical industrial city in northern China, and a total of 57 VOCs were measured for analysis. The average VOC concentrations were 54.4 µg·m−3, with the highest concentrations in autumn (58.4 µg·m−3). Ambient VOCs in spring, summer and autumn were all dominated by alkanes (66.8%), with contributions of 70.3%, 66.3% and 63.8%, respectively. The top five concentrations of total VOCs were isopentane (19.0%), ethane (9.5%), n-butane (8.1%), benzene (7.9%) and propane (5.2%), indicating that vehicle exhaust and coal combustion are the main sources of VOCs. Source apportionment by principal component analysis showed that vehicle exhaust (27.5%) and coal combustion (23.5%) were the main sources of VOCs in Changzhi, followed by industrial production (17.4%), solvent evaporation (13.5%), liquefied petroleum gas/natural gas leaking (9.5%), and biogenic emissions (8.7%). Sources of coal combustion and vehicle exhaust contributed more VOCs than industrial production. The carcinogenic risks of benzene (3.4 × 10−5) and ethylbenzene (2.2 × 10−6) were higher than the limit levels (1 × 10−6). Coal combustion contributed most (25.3%) to the carcinogenic risks because of its high VOC emissions. In an industrial city such as Changzhi, vehicle exhaust and coal combustion have become major sources of ambient air VOCs owing to the increasingly stringent industrial standards. Therefore, VOCs from vehicle exhaust and coal combustion also need to take into account mitigation measures for VOCs from the perspective of source contribution to health risk.

Characteristics of VOCs and Formation Potentials of O3 and SOA in Autumn and Winter in Tongchuan, China

Volatile organic compounds (VOCs) are the main precursors of tropospheric O3 and secondary organic aerosol (SOA), which can enhance atmospheric oxidation, promote the formation of secondary pollutants, and affect regional air quality and human health. In order to gain insights on VOCs characteristics and their potentials for O3 and SOA formation, the volume fraction of 102 VOCs in autumn and winter in the urban area of Tongchuan were monitored using the TH-300B online monitoring system. The maximum incremental reactivity (MIR) coefficient and the fractional aerosol coefficient (FAC) were used to estimate the ozone formation potential (OFP) and SOA formation potential (SOAFP), respectively. The φ(TVOC, total VOCs) were (50.52±16.81)×10-9 in autumn and (63.21±35.24)×10-9 in winter. The OFPs were 138.43×10-9 in autumn and 137.123×10-9 in winter, and the SOAFPs were 3.098 μg·m-3 and 0.612 μg·m-3, respectively. Alkanes (26.19%) and aromatics (26.04%) were the most abundant species in autumn, and alkanes (48.88%) were the most abundant species in winter. Trans-2-pentene, toluene, and m/p-xylene were the most reactive species in terms of OFPs in autumn, and ethylene, acetylene, and propylene were the top three species contributing to the total OFPs in winter. Toluene, m/p-xylene, and ethylbenzene contributed the most to the total SOAFPs in both of autumn and winter. Traffic emissions were considered as the major source of VOCs in both seasons. VOCs from biomass/coal combustion emissions showed seasonal differences, which were more prominent in winter. The results can provide references for the "one city, one policy" to mitigate regional VOCs pollution and improve ambient air quality.

Characteristics of Volatile Organic Compounds in the Pearl River Delta Region, China: Chemical Reactivity, Source, and Emission Regions

Volatile organic compounds (VOCs) are important precursors of photochemical ozone and secondary organic aerosol (SOA). Here, hourly variations of ambient VOCs were monitored with an online system at an urban site (Panyu, PY) in the Pearl River Delta region during August–September of 2020 in order to identify reactive VOC species and major sources of VOCs, OH loss rate (LOH), SOA formation potential (SOAFP), and corresponding emission source regions. The average concentration of VOCs at PY was 31.80 ± 20.82 ppbv during the campaign. The C2–C5 alkanes, aromatics, and ≥C6 alkanes contributed for the majority of VOC, alkenes and aromatics showed the highest contribution to LOH and SOAFP. Further, m/p-xylene, propene, and toluene were found to be the top three most reactive anthropogenic VOC species, with respective contributions of 11.6%, 6.1%, and 5.8% to total LOH. Toluene, m/p-xylene, and o-xylene constituted a large fraction of calculated SOAFP. Seven major sources were identified by using positive matrix factorization model. Vehicle exhaust made the most significant contribution to VOCs, followed by liquefied petroleum gas and combustion sources. However, industrial-related sources (including industrial solvent use and industrial process emission) had the largest contribution to LOH and SOAFP. By combining source contribution with wind direction and wind speed, the regions of different sources were further identified. Based on high-resolution observation data during ozone pollution, this study clearly exhibits key reactive VOC species and the major emission regions of different VOC sources, and thus benefits the accurate emission control of VOCs in the near future.

Research advance in gas detection of volatile organic compounds released in rice quality deterioration process

Rice quality deterioration will cause grievous waste of stored grain and various food safety problems. Gas detection of volatile organic compounds (VOCs) produced by deterioration is a nondestructive detection method to judge rice quality and alleviate rice spoilage. This review discussed the research advance of VOCs detection in terms of nondestructive detection methods of rice quality deterioration, applications of VOCs in grain detection, inspection of characteristic gas produced during rice spoilage, rice deterioration prevention and control, and detection of VOCs released by rice mildew and insect attack. According to the main causes of rice quality deterioration and major sources of VOCs with off-odor generated during rice storage, deterioration can be divided into mold and insect infection. The results of literature manifested that researches mainly focused on the infection of Aspergillus in the mildew process and the attack of certain pests in recent years, thus the research scope was limited. In this paper, the gas detection methods combined with the chemometrics to qualitatively analyze the VOCs, as well as the correlation with the number of colonies and insects were further studied based on the common dominant strains during rice mildew, that is, Aspergillus and Penicillium fungi, and the common pests during storage, that is, Sitophilus oryzae and Rhyzopertha dominica. Furthermore, this paper pointed out that the quantitative determination of characteristic VOCs, the numeration relationship between VOCs and the degree of mildew and insect infestation, the further expansion of detection range, and the application of degraded rice should be the spotlight of future research.

Pollution Characteristics and Source Analysis of Atmospheric VOCs in the Coastal Background of the Pearl River Delta

As an important precursor of ozone, volatile organic compounds (VOCs) have attracted much attention. This study analyzed the temporal variation and composition of atmospheric VOCs in the coastal background of the Pearl River Delta, using real-time online monitoring data of VOCs obtained at the Yangmeikeng Ecological Environment Monitoring Station from August 2019 to July 2020. The major sources of VOCs were identified using a receptor model based on the PMF (positive matrix factorization) and HYSPLIT (hybrid single particle Lagrangian integrated trajectory) models. The results showed that the annual mean concentration of anthropogenic VOCs in the coastal background area of the Pearl River Delta was 9.30×10-9(volume fraction). There was obvious seasonal variation of VOCs in this area, with higher values in autumn and winter and lower values in summer. The coastal background area of the Pearl River Delta exhibited a different diurnal variation pattern to that of cities and other backgrounds. While the peak of VOCs concentration mainly occurred in the morning, from 10:00 to 11:00, concentration remained at a low level during the early morning and after 15:00. Ethylene, propylene, toluene, isopentane, isoprene, m/p-xylene, n-butane, and acetylene were the key species that affected the chemical composition of VOCs. The air masses affecting the coastal background area of the Pearl River Delta were mainly short-distance air masses from elsewhere in the province (25%), ocean air masses (27%), coastal air masses (31%), and inland air masses outside the province (17%). Among them, the average concentration of VOCs was lowest under the influence of ocean air masses, which is mainly affected by the mixed source of ship emissions and aging VOCs, gasoline volatilization, and vehicle emissions. In comparison, the concentration level of VOCs increased by 70.1% to 148.8% under the influence of other air masses. The transmission effects of industrial sources, LNG and LPG volatiles, and petrochemical sources were more prominent. Generally, the atmosphere of coastal background areas was severely affected by anthropogenic pollution, especially by air pollution masses transported from the land, while the impact of pollution by ships near shore and tourist traffic cannot be ignored.

Characteristics and Sources of VOCs at Different Ozone Concentration Levels in Tianjin

To further study the effect of volatile organic compounds (VOCs) on ozone pollution, the characteristics and sources of VOCs at different ozone (O3) concentration levels were analyzed, using high-resolution online monitoring data obtained from Tianjin in the summer of 2019. Results showed that VOCs concentrations were 32.94, 38.10, 42.41, and 47.12 μg ·m-3, when the O3 concentration levels were categorized as excellent, good, light pollution, and moderate pollution, respectively. VOCs were composed of alkanes, alkenes, alkynes and aromatics, which accounted for 61.72%-63.36%, 14.96%-15.51%, 2.73%-4.13%, and 18.53%-19.10%, respectively, of VOCs concentrations at different O3 concentration levels. Among them, the proportion of alkanes was slightly higher when O3 concentration was categorized as good or light pollution, alkenes and alkynes accounted for the highest proportion when O3 concentration was excellent, and the proportion of aromatics was highest during periods of moderate pollution. The main VOCs species were propane, ethane, ethylene, toluent, n-butane, isopentane, m/p-xylene, propylene, acetylene, n-hexane, isobutene, benzene, n-pentane, isoprene, and 1,2,3-trimethylbenzene. The concentration percentage of isopentane, n-pentane, benzene, ethylene, propylene, n-butane, and isobutane increased gradually as O3 concentration increased. Significant increases in isoprene and 1,2,3-trimethylbenzene were observed during periods of light and moderate pollution. Alkenes and aromatics had higher ozone formation potential (OFP), and the contribution of alkenes to OFP declined as the O3 level rose, whereas that of aromatics increased. Ethylene, propylene, m/p-xylene, 1,2,3-trimethylbenzene, toluene, isoprene, trans-2-butene, and cis-2-pentene were the key species for O3 generation, and the contribution ratio of 1,2,3-trimethylbenzene, isoprene, propylene, and ethylene to OFP increased significantly during light or moderate O3 pollution. Positive matrix factorization was applied to estimate the source contributions of VOCs. Automobile exhaust, solvent usage, liquefied petroleum gas (LPG)/gasoline evaporation, combustion, petrochemical industrial emissions, natural sources, and other industrial emissions were identified as major sources of VOCs in summer. As O3 concentration level rose, the contribution percentage of automobile exhaust, LPG/gasoline evaporation, petrochemical industrial emissions, and natural sources increased gradually, whereas the contribution of combustion and other industrial emissions decreased overall. The contribution of solvent usage was lower when O3 levels indicated light or moderate pollution than when it was good.